In vivo organ mass of Korean adults obtained from whole-body magnetic resonance data

Prediction of exophthalmos by body mass index for craniofacial reconstruction: consequences for cold cases

It is inconvenient for a forensic practitioner to gather population-specific data before performing a facial reconstruction. The inconvenience may defeat the point of creating the reconstruction. The objective of this study was to evaluate a non-population-dependent method of determining exophthalmos. The protrusion of the eyeball is known to vary with the contents of the orbital cavity based on bony orbital resorption or increased or decreased fat contents, as well as according to relative eyeball size. Of use are available statistics on body mass index, and this is discussed within the context of eyeball protrusion. A weak positive correlation (0.3263) between the body mass index of the country where the study originated, and the degree of exophthalmos was found. The results suggest that eyeball protrusion rates can be established according to body mass index, and this framework may be more useful considering conventional police practices.

Korean-specific iodine S values for use in internal dosimetry

The use of iodine S values derived using the International Commission Radiological Protection (ICRP) phantoms may introduce significant bias in internal dosimetry for Koreans due to anatomical variability. In the current study, we produced an extensive dataset of Korean S values for selected five iodine radioisotopes (I-125, I-129, I-131, I-133, and I-134) for use in radiation protection. To calculate S values, we implemented Monte Carlo simulations using the Mesh-type Reference Korean Phantoms (MRKPs), developed in a high-quality/fidelity mesh format. Noticeable differences were observed in S value comparisons between the Korean and ICRP reference phantoms with ratios (Korean/ICRP) widely ranging from 0.16 to 6.2. The majority of S value ratios were lower than the unity in Korean phantoms (interquartile range =0.47-1.28; mean = 0.96; median = 0.69). The S values provided in the current study will be extensively utilized in iodine internal dosimetry for Koreans.

A dosimetric comparison of systemic peptide receptor radionuclide therapy and intra-arterial peptide receptor radionuclide therapy in patients with liver dominant gastroenteropancreatic neuroendocrine tumours

OBJECTIVES

Intra-arterial radionuclide therapy (IART) treatment allows direct delivery of 177 Lu-DOTATATE to the overexpressed somatostatin-positive neuroendocrine liver metastases, which led to higher tumour concentration compared with systemic radionuclide therapy (SRT). The aim was to evaluate and compare the absorbed doses of both IART and SRT to organs and hepatic metastatic sites.

METHODS

A total of 48 patients received SRT and IART. In SRT, activity was administered intravenously, whereas in IART, activity was administered directly into hepatic arteries. The sequential whole-body images were acquired at 2, 4, 24, 72 and 160 h. The reconstructed whole-body planar and single-photon emission computed tomography-computed tomography images were processed using the Dosimetry Toolkit for the estimation of normalized cumulated activity in the organs and tumour lesions. The absorbed dose was computed using OLINDA EXM 2.0 software.

RESULTS

The median absorbed dose (mGy/MBq) of kidneys and spleen in IART was compared with SRT and found to be decreased by 30.7% ( P  = 0.03) and 37.5% ( P  = 0.08), whereas it was found to be increased by 40% ( P  = 0.26) and 8.1% ( P  = 0.28) in the liver and lungs. The median dose (mGy/MBq) of tumours determined in IART was found to be increased by 62.2% ( P  = 0.04).

CONCLUSION

IART with 177 Lu-DOTATATE significantly increases tumour dose while reducing overall systemic toxicity in comparison to SRT treatment. After considering the maximum tolerance limit of kidneys in peptide receptor radionuclide therapy, the number of treatment cycles and injected activity can be optimized further with IART for better response and survival.

Analysis of absorbed dose in radioimmunotherapy with 177Lu-trastuzumab using two different imaging scenarios: a pilot study

OBJECTIVES

Internal organ dosimetry is an important procedure to demonstrate the reliable application of 177Lu-trastuzumab radioimmunotherapy for human epidermal growth factor receptor-positive metastatic breast cancers. We are reporting the first human dosimetry study for 177Lu-trastuzumab. Another objective of our study was to calculate and compare the absorbed doses for normal organs and tumor lesions in patients before radioimmunotherapy with 177Lu-trastuzumab using two different imaging scenarios.

METHODS

Eleven patients (48.27 ± 8.95 years) with a history of metastatic breast cancer were included in the study. Postadministration of 177Lu-trastuzumab (351.09 ± 23.89 MBq/2 mg), acquisition was performed using planar and hybrid imaging scenarios at 4, 24, 72 and 168 h. Single-photon emission computed tomography/computed tomography imaging was performed at 72 h postinjection. Acquired images were processed using Dosimetry Toolkit software for the estimation of normalized cumulated activity in organs and tumor lesions. OLINDA/EXM 2.0 software was used for absorbed dose calculation in both scenarios.

RESULTS

Significant difference in normalized cumulated activity and the absorbed dose is noted between two imaging scenarios for the organs and tumor lesions (P < 0.05). Mean absorbed dose (mGy/MBq) estimated from heart, lungs, liver, spleen, kidney, adrenal, pancreas and colon using planar and hybrid scenarios were 0.81 ± 0.19 and 0.63 ± 0.17; 0.75 ± 0.13 and 0.32 ± 0.06; 1.26 ± 0.25 and 1.01 ± 0.17; 0.68 ± 0.22 and 0.53 ± 0.16; 0.91 ± 0.3 and 0.69 ± 0.24; 0.18 ± 0.04 and 0.11 ± 0.02; 0.25 ± 0.22 and 0.09 ± 0.02 and 0.75 ± 0.61 and 0.44 ± 0.28, respectively.

CONCLUSIONS

On the basis of our dosimetric evaluation, we concluded that radioimmunotherapy with 177Lu-trastuzumab is well tolerated to be implemented in routine clinical practice against HER2 positive metastatic breast cancer. Liver is the main critical organ at risk. Hybrid scenario demonstrated significantly lower absorbed doses in organs and tumors compared to the multiplanar method.

Radiation dose from computed tomography scans for Korean pediatric and adult patients

Background

In recent events of the Coronavirus Disease 2019 (COVID-19) pandemic, CT scans are being globally used as a complement to the reverse-transcription polymerase chain reaction (RT-PCR) tests. It will be important to be aware of major organ dose levels, which are more relevant quantity to derive potential long-term adverse effect, for Korean pediatric and adult patients undergoing CT for COVID-19.

Materials and Methods

We calculated organ dose conversion coefficients for Korean pediatric and adult CT patients directly from Korean pediatric and adult computational phantoms combined with Monte Carlo radiation transport techniques. We then estimated major organ doses delivered to the Korean child and adult patients undergoing CT for COVID-19 combining the dose conversion coefficients and the international survey data. We also compared our Korean dose conversion coefficients with those from Caucasian reference pediatric and adult phantoms.

Results and discussion

Based on the dose conversion coefficients we established in this study and the international survey data of COVID-19-related CT scans, we found that Korean 7-year-old child and adult males may receive about 4 - 32 mGy and 3 - 21 mGy of lung dose, respectively. We learned that the lung dose conversion coefficient for the Korean child phantom was up to 1.5-fold greater than that for the Korean adult phantom. We also found no substantial difference in dose conversion coefficients between Korean and Caucasian phantoms.

Conclusion

We estimated radiation dose delivered to the Korean child and adult phantoms undergoing COVID-19-related CT examinations. The dose conversion coefficients derived for different CT scan types can be also used universally for other dosimetry studies concerning Korean CT scans. We also confirmed that the Caucasian-based CT organ dose calculation tools may be used for the Korean population with reasonable accuracy.

Determining Average Linear Dimension and Volume of Korean Lungs for Lung Phantom Construction

ABSTRACT

The purpose of this study was to determine the average size and volume of lungs and to simulate the morphology of internal organs for the development of a Korean adult lung phantom. The body-size data of 2,195 males and 2,293 females aged between 20 and 60 y were included to calculate the average physical dimensions. Two hundred datasets of computed tomography corresponding to the average physique range were collected to measure the average linear dimensions (the length of x, y, and z-axis) of lungs. One set of lung CT images was finally obtained and converted to three-dimensional (3D) format. To confirm the validity of the new lung model, physical lung phantoms were constructed using International Commission on Radiation Units and Measurements (ICRU) density and similar density to what was obtained from the human CT image and then compared with the Lawrence Livermore National Laboratory (LLNL) phantom. The mean size of the chest width and thickness was 31.8 ± 2.8 and 21.4 ± 1.9 cm for males and 28.0 ± 1.6 cm and 19.4 ± 2.0 cm for females, respectively. The standard deviation of the lung dimension in this group was ± 3.0 cm in length, ± 0.8 cm in width, and ± 2.27 cm in depth. The two modified lung phantoms showed highly accurate geometry and linear attenuation coefficient vs. those of the LLNL phantom. The difference in CT number was ± 2% HU for the LLNL phantom and ± 4% HU for the human CT image based on a CT examination conducted using the chest CT protocol. Moreover, both lungs weighed 734 g to 1,246 g, within the range of the reference value of the ICRU report. These results demonstrate that a new lung model based on average linear dimension measurement in a group with average physique simulated the features and physical properties of real human lungs and facilitated further studies for phantom construction.

Organ dose conversion coefficients calculated for Korean pediatric and adult voxel phantoms exposed to external photon fields

Background

Dose conversion coefficients (DCCs) have been commonly used to estimate radiation dose absorbed in human organs from physical measurements of fluence or kerma. The International Commission on Radiological Protection (ICRP) reported a library of DCCs but few studies were conducted on their applicability to non-Caucasian populations. In the present study, we collected a total of eight Korean pediatric and adult voxel phantoms to calculate organ DCCs for idealized external photon irradiation geometries.

Materials and methods

We adopted one pediatric female phantom (ETRI Child), two adult female phantoms (KORWOMAN and HDRK Female), and five adult male phantoms (KORMAN, ETRI Man, KTMAN1, KTMAN2, and HDRK Man). A general-purpose Monte Carlo radiation transport code, MCNPX2.7, was employed to calculate dose conversion coefficients for 13 major radiosensitive organs in six irradiation geometries (antero-posterior, postero-anterior, right lateral, left lateral, rotational, and isotropic) and 33 photon energy bins (0.01 - 20 MeV).

Results and discussion

The DCCs for major radiosensitive organs (e.g., lungs and colon) in AP geometry reasonably agreed across the eight Korean phantoms whereas those for deep-seated organs (e.g., gonads) significantly varied. DCCs of the child phantom were overall greater than those of the adult phantoms. Comparison with the ICRP Publication 116 data showed reasonable agreements with Korean phantom-based data. The variations in organ DCCs were well explained using the distribution of organ depths from the phantom surface.

Conclusion

A library of dose conversion coefficients for major radiosensitive organs in a series of pediatric and adult Korean voxel phantoms was established and compared with the reference data from ICRP. Comparison with the data from the ICRP reference adult voxel phantoms showed that our Korean phantom-based data is overall in a reasonable agreement with the ICRP reference data.

Mesh-type reference Korean phantoms (MRKPs) for adult male and female for use in radiation protection dosimetry

In the present study, to overcome the dosimetric limitations of the previous voxel-type reference Korean computational phantoms due to their limited voxel resolutions (i.e. on the order of millimeters) and the nature of voxel geometry, a pair of new reference Korean phantoms, called mesh-type reference Korean phantoms (MRKPs), were developed for the adult male and female in a high-quality/fidelity mesh format. The developed phantoms include all target and source regions required for effective dose calculation, even micrometer-scale target and source regions of the respiratory and alimentary tract organs, skin, urinary bladder, and eye lens. The developed phantoms, which are in either the polygon-mesh (PM) format or the tetrahedral-mesh (TM) format as necessary, can be directly used in several general-purpose Monte Carlo codes (e.g. Geant4, MCNP6, and PHITS) without voxelization. In order to understand the dosimetric impact of the new phantoms, the dose coefficients (=fluence-to-effective dose conversion coefficients) were calculated for photons and electrons with energies ranging from 10 keV to 10 GeV for the anterior-posterior (AP) irradiation geometry and compared with those of the previous voxel-type reference Korean phantoms. The results demonstrate that the effective dose coefficients of the MRKPs were generally similar to those of the previous voxel-type reference phantoms for photons; however, for electrons, significant differences were observed at energies lower than 1 MeV that were mainly due to the explicit definition of the 50 µm-thick radiosensitive target layer in the skin of the new mesh phantoms.

Measurement of fat fraction in the human thymus by localized NMR and three-point Dixon MRI techniques

PURPOSE

To develop a protocol to non-invasively measure and map fat fraction, fat/(fat+water), as a function of age in the adult thymus for future studies monitoring the effects of interventions aimed at promoting thymic rejuvenation and preservation of immunity in older adults.

MATERIALS AND METHODS

Three-dimensional spoiled gradient echo 3T MRI with 3-point Dixon fat-water separation was performed at full inspiration for thymus conspicuity in 36 volunteers 19 to 56 years old. Reproducible breath-holding was facilitated by real-time pressure recording external to the console. The MRI method was validated against localized spectroscopy in vivo, with ECG triggering to compensate for stretching during the cardiac cycle. Fat fractions were corrected for T₁ and T₂ bias using relaxation times measured using inversion recovery-prepared PRESS with incremented echo time.

RESULTS

In thymus at 3 T, T_1water = 978 ± 75 ms, T_1fat = 323 ± 37 ms, T_2water = 43.4 ± 9.7 ms and T_2fat = 52.1 ± 7.6 ms were measured. Mean T₁-corrected MRI fat fractions varied from 0.2 to 0.8 and were positively correlated with age, weight and body mass index (BMI). In subjects with matching MRI and MRS fat fraction measurements, the difference between these measurements exhibited a mean of -0.008 with a 95% confidence interval of (0.123, -0.138).

CONCLUSIONS

3-point Dixon MRI of the thymus with T₁ bias correction produces quantitative fat fraction maps that correlate with T₂-corrected MRS measurements and show age trends consistent with thymic involution.

Software-assisted dosimetry in peptide receptor radionuclide therapy with 177Lutetium-DOTATATE for various imaging scenarios

In peptide receptor radionuclide therapy (PRRT) of patients with neuroendocrine neoplasias (NENs), intratherapeutic dosimetry is mandatory for organs at risk (e.g. kidneys) and tumours. We evaluated commercial dosimetry software (Dosimetry Toolkit) using varying imaging scenarios, based on planar and/or tomographic data, regarding the differences in calculated organ/tumour doses and the use for clinical routines. A total of 16 consecutive patients with NENs treated by PRRT with 177Lu-DOTATATE were retrospectively analysed. Single-photon emission computed tomography (SPECT)/low-dose computed tomography (CT) of the thorax and abdomen and whole body (WB) scintigraphy were acquired up to 7 days p.i. (at a maximum of five imaging time points). Different dosimetric scenarios were evaluated: (1) a multi-SPECT-CT scenario using SPECT/CT only; (2) a planar scenario using WB scintigraphy only; and (3) a hybrid scenario using WB scintigraphy in combination with a single SPECT/low-dose CT. Absorbed doses for the kidneys, liver, spleen, lungs, bladder wall and tumours were calculated and compared for the three different scenarios. The mean absorbed dose for the kidneys estimated by the multi-SPECT-CT, the planar and the hybrid scenario was 0.5 ± 0.2 Sv GBq-1, 0.8 ± 0.4 Sv GBq-1 and 0.6 ± 0.3 Sv GBq-1, respectively. The absorbed dose for the residual organs was estimated higher by the planar scenario compared to the multi-SPECT-CT or hybrid scenario. The mean absorbed tumour doses were 2.6 ± 1.5 Gy GBq-1 for the multi-SPECT-CT, 3.1 ± 2.2 Gy GBq-1 for the hybrid scenario and 5.3 ± 6.3 Gy GBq-1 for the planar scenario. SPECT-based dosimetry methods determined significantly lower kidney doses than the WB scintigraphy-based method. Dosimetry based completely on SPECT data is time-consuming and tedious. Approaches combining SPECT/CT and WB scintigraphy have the potential to ensure compromise between accuracy and user-friendliness.

Dose Conversion Coefficients Based on Taiwanese Reference Phantoms and Monte Carlo Simulations for Use in External Radiation Protection

Reference phantoms are widely applied to evaluate the radiation dose for external exposure. However, the frequently used reference phantoms are based on Caucasians. Dose estimation for Asians using a Caucasian phantom can result in significant errors. This study recruited 40 volunteers whose body sizes are close to the average Taiwanese population. Magnetic resonance imaging was performed to obtain the organ volume for construction of the Taiwanese reference man (TRM) and Taiwanese reference woman (TRW). The dose conversion coefficients (DCC) resulting from photo beams in anterior-posterior, posterior-anterior, right-lateral, left-lateral, and isotropic irradiation geometries were estimated. In the anterior-posterior geometry, the mean DCC differences among organs between the TRM and ORNL phantom at 0.1, 1, and 10 MeV were 7.3%, 5.8%, and 5.2%, respectively. For the TRW, the mean differences from the ORNL phantom at the three energies were 10.6%, 7.4%, and 8.3%. The DCCs of the Taiwanese reference phantoms and the ORNL phantom presented similar trends in other geometries. The torso size of the phantom and the mass and geometric location of the organ have a significant influence on the DCC. The Taiwanese reference phantoms can be used to establish dose guidelines and regulations for radiation protection from external exposure.

HDRK-Woman: whole-body voxel model based on high-resolution color slice images of Korean adult female cadaver

In a previous study, we constructed a male reference Korean phantom; HDRK-Man (High-Definition Reference Korean-Man), to represent Korean adult males for radiation protection purposes. In the present study, a female phantom; HDRK-Woman (High-Definition Reference Korean-Woman), was constructed to represent Korean adult females. High-resolution color photographic images obtained by serial sectioning of a 26 year-old Korean adult female cadaver were utilized. The body height and weight, the skeletal mass, and the dimensions of the individual organs and tissues were adjusted to the reference Korean data. The phantom was then compared with the International Commission on Radiological Protection (ICRP) female reference phantom in terms of calculated organ doses and organ-depth distributions. Additionally, the effective doses were calculated using both the HDRK-Man and HDRK-Woman phantoms, and the values were compared with those of the ICRP reference phantoms.

A polygon-surface reference Korean male phantom (PSRK-Man) and its direct implementation in Geant4 Monte Carlo simulation

Even though the hybrid phantom embodies both the anatomic reality of voxel phantoms and the deformability of stylized phantoms, it must be voxelized to be used in a Monte Carlo code for dose calculation or some imaging simulation, which incurs the inherent limitations of voxel phantoms. In the present study, a voxel phantom named VKH-Man (Visible Korean Human-Man), was converted to a polygon-surface phantom (PSRK-Man, Polygon-Surface Reference Korean-Man), which was then adjusted to the Reference Korean data. Subsequently, the PSRK-Man polygon phantom was directly, without any voxelization process, implemented in the Geant4 Monte Carlo code for dose calculations. The calculated dose values and computation time were then compared with those of HDRK-Man (High Definition Reference Korean-Man), a corresponding voxel phantom adjusted to the same Reference Korean data from the same VKH-Man voxel phantom. Our results showed that the calculated dose values of the PSRK-Man surface phantom agreed well with those of the HDRK-Man voxel phantom. The calculation speed for the PSRK-Man polygon phantom though was 70-150 times slower than that of the HDRK-Man voxel phantom; that speed, however, could be acceptable in some applications, in that direct use of the surface phantom PSRK-Man in Geant4 does not require a separate voxelization process. Computing speed can be enhanced, in future, either by optimizing the Monte Carlo transport kernel for the polygon surfaces or by using modern computing technologies such as grid computing and general-purpose computing on graphics processing units programming.

Differences between brain mass and body weight scaling to height: potential mechanism of reduced mass-specific resting energy expenditure of taller adults

Adult resting energy expenditure (REE) scales as height( approximately 1.5), whereas body weight (BW) scales as height( approximately 2). Mass-specific REE (i.e., REE/BW) is thus lower in tall subjects compared with their shorter counterparts, the mechanism of which is unknown. We evaluated the hypothesis that high-metabolic-rate brain mass scales to height with a power significantly less than that of BW, a theory that if valid would provide a potential mechanism for height-related REE effects. The hypothesis was tested by measuring brain mass on a large (n = 372) postmortem sample of Thai men. Since brain mass-body size relations may be influenced by age, the hypothesis was secondarily explored in Thai men age < or =45 yr (n = 299) and with brain magnetic resonance imaging (MRI) studies in Korean men (n = 30) age > or =20<30 yr. The scaling of large body compartments was examined in a third group of Asian men living in New York (NY, n = 28) with MRI and dual-energy X-ray absorptiometry. Brain mass scaled to height with a power (mean +/- SEE; 0.46 +/- 0.13) significantly smaller (P < 0.001) than that of BW scaled to height (2.36 +/- 0.19) in the whole group of Thai men; brain mass/BW scaled negatively to height (-1.94 +/- 0.20, P < 0.001). Similar results were observed in younger Thai men, and results for brain mass/BW vs. height were directionally the same (P = 0.09) in Korean men. Skeletal muscle and bone scaled to height with powers similar to that of BW (i.e., approximately 2-3) in the NY Asian men. Models developed using REE estimates in Thai men suggest that brain accounts for most of the REE/BW height dependency. Tall and short men thus differ in relative brain mass, but the proportions of BW as large compartments appear independent of height, observations that provide a potential mechanistic basis for related differences in REE and that have implications for the study of adult energy requirements.

Development of a Korean adult male computational phantom for internal dosimetry calculation

A Korean adult male computational phantom was constructed based on the current anthropometric and organ volume data of Korean average adult male, and was applied to calculate internal photon dosimetry data. The stylised models of external body, skeleton, and a total of 13 internal organs (brain, gall bladder, heart, kidneys, liver, lungs, pancreas, spleen, stomach, testes, thymus, thyroid and urinary bladder) were redesigned based on the Oak Ridge National Laboratory (ORNL) adult phantom. The height of trunk of the Korean phantom was 8.6% less than that of the ORNL adult phantom, and the volumes of all organs decreased up to 65% (pancreas) except for brain, gall bladder wall and thymus. Specific absorbed fraction (SAF) was calculated using the Korean phantom and Monte Carlo code, and compared with those from the ORNL adult phantom. The SAF of organs in the Korean phantom was overall higher than that from the ORNL adult phantom. This was caused by the smaller organ volume and the shorter inter-organ distance in the Korean phantom. The self SAF was dominantly affected by the difference in organ volume, and the SAF for different source and target organs was more affected by the inter-organ distance than by the organ volume difference. The SAFs of the Korean stylised phantom differ from those of the ORNL phantom by 10-180%. The comparison study of internal dosimetry will be extended to tomographic phantom and electron source in the future.